1. Field of the Invention
The invention relates to an engine misfire detection system for use in a hybrid vehicle including a spark ignition type internal combustion engine having a plurality of cylinders, and a motor-generator.
2. Description of Related Art
As a misfire detection system of an internal combustion engine installed on a hybrid vehicle, a system as described in Japanese Patent Application Publication No. 2006-266253 (JP 2006-266253 A) is known. In order to accurately determine the presence or absence of misfire even in the case where the ignition timing of the engine is retarded, the system of JP 2006-266253 A sequentially computes fluctuations in the engine speed at the time of ignition in each cylinder, and determines misfire by comparing the engine speed between the first rotation and the second rotation. Other related-art documents related to this invention include Japanese Patent Application Publication No. 2007-30710 (JP 2007-30710 A) and Japanese Patent Application Publication No. 2009-174397 (JP 2009-174397 A).
Generally, as the number of cylinders of the internal combustion engine is larger, the interval of combustion between the cylinders becomes shorter. Therefore, as the number of cylinders increases, combustion overlapping is more likely to occur, namely, torque produced by combustion in a certain cylinder is more likely to overlap torque produced by combustion in a cylinder that reaches the ignition timing next. Further, if the ignition timing is retarded, the combustion timing is delayed, and therefore, the influence of the combustion overlapping expands. Due to the influence of the combustion overlapping, it becomes difficult to determine which one of the cylinders undergoes fluctuations in the engine speed when misfire is determined, as in the system of JP 2006-266253; therefore, the determination accuracy may deteriorate.